High-Resolution Seismic Survey To Evaluate Groundwater Potential At A Proposed Electric Power Generation Facility

High resolution seismic reflection profiling was effective in delineating geologic units within the<br>upper 200 ft at a proposed power plant site in southern Minnesota. Glacial activity is responsible for the<br>topography of the bedrock surface evident on seismic reflection data across this site. Gravel and sands<br>deposited during glacial retreat into bedrock lows can provide a significant source of water for a variety<br>of residential, commercial, and municipal applications. Selection of power generation plant sites is<br>routinely based on availability of fuel, proximity to existing power grid, and a ready source of water. In<br>this case the first two criteria were met; the purpose of the seismic survey was to evaluate and direct a<br>drilling program that would establish the third. Dominant frequencies of the nominal 24-fold data<br>acquired along two lines are, on the average, in excess of 150 Hz, which provides practical vertical bed<br>resolutions (~½ wavelength) on the order of 15 ft. Bedding geometries interpreted from CMP stacked<br>sections were consistent with several boreholes located around this 80-acre site. Several apparent structural<br>features interpreted at bedrock depth on the stacked sections were mapped as potential water<br>sources. The bedrock low interpreted from drill data was observed on the stacked seismic section but<br>was confined to a much smaller area than mapped using the few scattered drill holes. A complex bedding<br>geometry associated with the advance and retreat of glaciers is evident on the seismic data above<br>the bedrock surface. Drilling confirmed the seismic interpretation and provided additional information<br>about the nature of the material within the bedrock lows. This proposed site was abandoned due to insufficient<br>quantities of gravel and coarse sands within the glacially sculpted bedrock lows.